<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div{
            display: flex;
            width: 800px;
            height: 300px;
            background-color: pink;
            /* 使用默认x轴  */
            flex-direction: row;
            /* 设置主轴上子元素的排列- 
            flex-start 头部对齐*/
            justify-content: flex-start;
            /* 尾部对齐（不会反转） */
            justify-content: flex-end;
            /* 居中对齐 */
            justify-content: center;
            /* 平分剩余空间(盒子左右相等) */
            justify-content: space-around;
            /* 先左右贴边，在平分剩余空间 */
            justify-content: space-between;
        }
         div span{
            width: 150px;
            height: 100px;
            background-color: gray;
        }
    </style>
</head>
<body>
    <div>
        <span>1</span>
        <span>2</span>
        <span>3</span>
        <span>3</span>
    </div>
</body>
</html>